# Math Help - Derivatives chain rule/velocity

1. ## Derivatives chain rule/velocity

I need to check my answers on part a, and see what's wrong on b. Also, what units do i use?

An abnormal projectile is shot in the air, so that after t seconds, its height in feet is $s(t)=14ln(-cos(\frac{x}{2}+1.67))+34$
a) find the velocity at times 0 and 5
b) When is it highest? When does it land?

I have the derivative as $-7tan(/frac{x}{2}+1.67)$
a) @t=0, 70.33 (units?)
@t=5, -11.6 (units?)

b) I wasn't totally sure how to do it, so I set the derivative equal to 0. I thought that that should give me the max height, but I came out with -3.34, which is obviously wrong. Did i make a math error or should I not have set it equal to 0? please help!

I have the derivative as $-7tan(/frac{x}{2})$
$-7tan(\frac{x}{2}+1.67)$